Machinery's Handbook, 31st Edition
2100
British Pipe Threads British Standard External and Internal Pipe Threads (Pressure-tight Joints) Metric and Inch Dimensions and Limits of Size BS 21:1973
Basic Diameters at Gage Plane
Gage Length
Tolerance + and −
Number of Useful Threads on Pipe for Basic Gage Length b
On Diameter of Parallel Int. Threads
Gage Plane to Face of Int. Taper Thread
No. of Threads per Inch a
Toler ance (+ and − )
Nominal Size
Major
Pitch Minor
Basic
(1) 0.9 (1) 0.9 (1) 1.3 (1) 1.3 (1) 1.8 (1) 1.8 (1) 2.3 (1) 2.3 (1) 2.3 (1) 2.3
0.071
7.723 7.142 6.561 (4 3 ∕ 8 ) 0.304 0.2812 0.2583 4.0 9.728 9.147 8.566 (4 3 ∕ 8 ) 0.383 0.3601 0.3372 4.0 13.157 12.301 11.445 (4 1 ∕ 2 ) 0.518 0.4843 0.4506 6.0 16.662 15.806 14.950 (4 3 ∕ 4 ) 0.656 0.6223 0.5886 6.4 20.955 19.793 18.631 (4 1 ∕ 2 ) 0.825 0.7793 0.7336 8.2 26.441 25.279 24.117 (5 1 ∕ 4 ) 1.041 0.9953 0.9496 9.5 33.249 31.770 30.291 (4 1 ∕ 2 ) 1.309 1.2508 1.1926 10.4 41.910 40.431 38.952 (5 1 ∕ 2 ) 1.650 1.5918 1.5336 12.7 47.803 46.324 44.845 (5 1 ∕ 2 ) 1.882 1.8238 1.7656 12.7 59.614 58.135 56.656 (6 7 ∕ 8 ) 2.347 2.2888 2.2306 15.9 75.184 73.705 72.226 (7 9 ∕ 16 ) 2.960 2.9018 2.8436 17.5 87.884 86.405 84.926 (8 15 ∕ 16 ) 3.460 3.4018 3.3436 20.6 113.030 111.551 110.072 (11) 4.450 4.3918 4.3336 25.4 138.430 136.951 135.472 (12 3 ∕ 8 ) 5.450 5.3918 5.3336 28.6 163.830 162.351 160.872 (12 3 ∕ 8 ) 6.450 6.3918 6.3336 28.6
(7 1 ∕ 8 )
(1 1 ∕ 4 )
28
{
1 ∕ 16
6.5
1.1
0.0028 0.071 0.0028 0.104 0.0041 0.104 0.0041 0.142 0.0056 0.142 0.0056 0.180 0.0071 0.180 0.0071 0.180 0.0071 0.180 0.0071 0.216 0.0085 0.216 0.0085 0.216 0.0085 0.216 0.0085 0.216
(7 1 ∕ 8 )
(1 1 ∕ 4 )
28
{
1 ∕ 8
6.5
1.1
(7 1 ∕ 4 )
(1 1 ∕ 4 )
19
{
1 ∕ 4
9.7
1.7
(7 1 ∕ 2 ) 10.1 (7 1 ∕ 4 ) 13.2 14.5 (7 1 ∕ 4 ) 16.8 (8 1 ∕ 4 ) (8) 19.1 (8 1 ∕ 4 ) 19.1
(1 1 ∕ 4 )
19
{
3 ∕ 8
1.7
(1 1 ∕ 4 )
14
{
1 ∕ 2
2.3
(1 1 ∕ 4 )
14
{
3 ∕ 4
2.3
(1 1 ∕ 4 )
1
11
{
2.9
(1 1 ∕ 4 )
11
{
1 1 ∕ 4
2.9
(1 1 ∕ 4 )
11
{
1 1 ∕ 2
2.9
(10 1 ∕ 8 )
(1 1 ∕ 4 )
2
11
{
23.4
2.9
(1 1 ∕ 2 )
(11 9 ∕ 16 )
(1 1 ∕ 2 )
11
{
2 1 ∕ 2
3.5
26.7
3.5
(1 1 ∕ 2 )
(12 15 ∕ 16 )
(1 1 ∕ 2 )
3
11
{
3.5
29.8
3.5
(1 1 ∕ 2 )
(15 1 ∕ 2 )
(1 1 ∕ 2 )
4
11
{
3.5
35.8
3.5
(1 1 ∕ 2 )
(17 3 ∕ 8 )
(1 1 ∕ 2 )
5
11
{
3.5
40.1
3.5
(1 1 ∕ 2 )
(17 3 ∕ 8 )
(1 1 ∕ 2 )
6
11
{
3.5 40.1 0.0085 a In the Standard BS 21:1973 the thread pitches in millimeters are as follows: 0.907 for 28 threads per inch, 1.337 for 19 threads per inch, 1.814 for 14 threads per inch, and 2.309 for 11 threads per inch. b This is the minimum number of useful threads on the pipe for the basic gage length; for the maximum and minimum gage lengths, the minimum numbers of useful threads are, respectively, greater and less by the amount of tolerance in the column to the left. The design of internally threaded parts shall make allowance for receiving pipe ends of up to the minimum number of useful threads corresponding to the maximum gage length; the minimum number of useful internal threads shall be no less than 80 percent of the minimum number of useful external threads for the minimum gage length. 3.5 Each basic metric dimension is given in roman figures (nominal sizes excepted) and each basic inch dimension is shown in italics directly beneath it. Figures in ( ) are numbers of turns of thread with metric linear equivalents given beneath. Taper of taper thread is 1 in 16 on diameter.
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